leetcode143. Reorder List

leetcode143. Reorder List

题意：

给定单链表L：L0≤L1≤... Ln-1≤Ln，
将其重新排序为：L0≤Ln≤L1≤Ln-1≤L2≤Ln-2≤...

思路：

第一次遍历把数组切成两半，然后吧右边的reverse，然后连接两个list，注意细节

ac代码：

C++

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void reorderList(ListNode* head) {
        if(!head || !head->next) return;
        ListNode* slow = head;
        ListNode* fast = head->next;
        
        //find middle,cut list
        while(fast && fast->next)
        {
            slow = slow->next;
            fast = fast->next->next;
        }
        ListNode* head2 = slow->next;
        slow->next = NULL;
        
        //reverse right part
        ListNode* p2 = head2->next;
        head2->next = NULL;
        ListNode* p1 = p2;
        while(p2)
        {
            p1 = p2->next;
            p2->next = head2;
            head2 = p2;
            p2 = p1;
        }
       
        for(p1 = head,p2 = head2;p1;)
        {
            auto t = p1->next;
            p1 = p1->next = p2;
            p2 = t;
        }       
    }
};

python